The present invention relates to methods for economic utilization of waste waters produced from water purification processing.
Water purification typically produces a first effluent of relatively “clean water” and a second effluent of “waste water” which includes unwanted contaminates. The softening of hard water by the removal of calcium and magnesium is required for both industrial and household use. Known water softening processes proceed either by way of ion-exchange, membrane softening or precipitation. In the ion-exchange processes, the calcium and magnesium ions are exchanged for sodium and regeneration of the ion-exchange resin is achieved with a large excess of NaCl. This process creates a regeneration effluent that is a relatively concentrated aqueous solution of sodium, calcium and magnesium chlorides. which has to be discarded. Consequently, this method requires disposal of considerable amounts of sodium, calcium and magnesium salts in solution.
Alternatively, it is possible to use weak acid resins which exchange hydrogen for calcium and magnesium, and to regenerate the spent resins with a mineral acid. While this method creates less waste water, it is more expensive and yields relatively acidic soft water which is corrosive. Meanwhile, membrane softening concentrates the calcium, magnesium salts and salts of other divalent ions to produce waste waters which require costly disposal.
The precipitation process has traditionally been carried out by the “lime soda” process in which lime is added to hard water to convert water soluble calcium bicarbonate into water insoluble calcium carbonate. This process also results in waste water which is difficult to filter and requires cumbersome treatment. My previously issued patent, U.S. Pat. No. 5,300,123 (which is incorporated herein by reference) relates to the purification of impure solid salts. Even this process produces salty waste water which must be disposed of.
The disposal of waste water has become an expensive problem for society. For example, approximately 1.61 billion gallons of waste water containing approximately 800,000 tons of mixed sodium, calcium, magnesium chlorides and sulfates is produced from water treatment operations and oil fields in the state of California alone. This waste water must be disposed of, costing the state of California millions of dollars each year. Meanwhile, the disposal of waste water has become even more problematic in other parts of the world. As a result, billions of dollars are spent each year toward efforts to dispose of waste waters. Accordingly, it would be highly advantageous to provide improved methods of disposing of salty waste waters. It would even be more advantageous to provide methods of using salty waste waters which provide a benefit to society, instead of simply disposing of the unwanted waste waters.
Wind erosion of soil is also a significant problem throughout the world. Due to small particle size and poor cohesion, finely divided soil is sensitive to the influence of wind. Such finely divided soil is found in agricultural lands, dunes, lake beds, construction sites and roads under construction. Erosion by wind causes dust formation and the loss of valuable matter such as seed, fertilizer and plantlets. Dust storms are a danger to traffic and a health risk to persons located in the vicinity. Moreover, the effects of wind erosion on soil can be enhanced by the influence of the sun and rain. The sun causes the evaporation of moisture from soil, thereby reducing the cohesion of finely divided soil. Erosion of the soil by rain is caused by rain washing away soil. This is a particular problem when agricultural soil is washed away, damaging plant life and making the soil unusable for agricultural purposes. Further, due to the influence of erosion by rain, the unprotected slopes of ditches, channels, dunes and roads may collapse or be washed away. Therefore, it is extremely important to prevent the effects of the sun, wind and water in eroding soil. As used herein, soil stabilization refers to the treatment of soils with chemicals to offset the tendencies of soils to be sensitive to small changes in the types of ions in the soil moisture as they affect the plasticity of the soil. For example, swelled clays, those with layers of “bound” water molecules, are more susceptible to movement under load. Soil stabilization of swelled clays can be effected by altering the types and/or amounts of ions in the soil mixture. It has been proposed that shift, drift and erosion of soil may be prevented by treating the surface layers of the soil with water dispersible high polymeric substances of a natural or synthetic nature. Examples of these high polymeric substances include starch ethers, hydrolyze polyacrylonitrile, polyvinyl alcohol and carboxymethyl cellulose. U.S. Pat. No. 3,077,054 discloses the use of polyvinyl acetate as an anti-erosion agent. U.S. Pat. No. 3,224,867 teaches the conditioning of soil with monostarch phosphate. U.S. Pat. No. 5,125,770 teaches treating the soil with a pre-gelatinized starch and a surfactant compound. Furthermore, it has been known to treat dirt roads with relatively pure solid sodium chloride, calcium chloride, and mixtures of the two.
There are several drawbacks to using these soil treating compounds. The polymers mentioned have a relatively high price and have potentially harmful environmental properties. In addition, the starch ethers are sensitive to washing out by rain water. As a result, their effectiveness as an anti-erosion agent is severely limited.
Another problem encountered throughout the world involves fungus. There are millions of acres of land in California, Arizona, New Mexico, Texas and the Sonora and Sinaloa areas of Mexico where crop production is almost impossible due to fungus, which attacks virtually all dicotyledonous plants, of which there are more than 2,000 species. These include cotton, alfalfa and citrus trees. The lack of productivity is due to excessive calcium carbonate in the soil which minimizes swelling to the point that carbon dioxide from decaying humus concentrates to more than about 3.2% CO3. where fungus thrives. These fungus, primarily Phytomatotrichum omnivorim (Shear) Duggar, have three stages of development called the mycelium, conidium and scelerotia. The first stage, referred to as mycelium, involves the development of a fine filament which branches out throughout the soil and forms a tight web around plant roots. After the filament reaches the soil surface, a white mat forms on the surface, referred to as conidium. When mature, the mycelium develops multicellular bodies called scelerotia which can extend to a depth of up to twelve feet into the soil.
About 1970, it was discovered that the addition of sodium to soil offsets the excess calcium in the soil. This increases the soil permeability and avoids the build-up of carbon dioxide that permits the root rot to flourish. Sodium chloride has been applied where the soil drains readily and the excess chloride and sodium are leached away by rainfall or irrigation. Sodium sulfate is preferable because 1) the sulfate supplies the nutrient sulfur, 2) the sulfate combines with calcium to form gypsum and gypsum soils typically do not support root rot, 3) gypsum buffers excess sodium assisting its leaching from the soil, and 4) there is no additional chloride residue which can leach into the water table. Unfortunately, sodium sulfate has always been too costly to be used to treat soil for farming. Recently, it has been suggested that solid mixtures of salts removed from water softening processes can be used to control root rot. However, salts removed from water by softening are still relatively expensive and the process of using salts recovered from waste water has not been adopted within the agricultural community.
Still another problem encountered in agriculture is that soil is often too high in sodium and/or too high in salinity. Farmland drainage and irrigation water are often unacceptably high in sodium. Irrigation waters containing high amounts of sodium salts versus calcium and/or magnesium salts can create a buildup of sodium in the soil. This excess sodium results in the dispersion of soil colloidal particles and an increase in soil pH. The dispersion of colloidal particles causes the soil to become hard and compact when dry with increased resistant to water infiltration and percolation. The sodium rich soil also becomes resistant to water penetration due to soil swelling when wet.
The total salinity of soil and irrigation water is also of concern. Salinity refers to the total salts within the water, with the significant positive ions (cations) in salinity being calcium, magnesium and sodium and the significant negative ions (anions) being chloride, sulfate and bicarbonate.
All irrigation water contains some dissolved salts. When soil has a high content of dissolved salts, or the irrigation waters have sufficient salts to increase the salinity of the soil, the soil has the tendency to hold the water instead of releasing the water for absorption by plant roots by osmotic pressure. Even if the soil contains plenty of moisture, plants will wilt because they cannot absorb necessary water.
Ironically, though there is an overabundance of waste waters that are contaminated with the salts of Na, K, Ca, Mg, Fe, Cl, SO4, and CO3 that, as discussed above, the disposal of which is extraordinarily expensive. Millions of dollars are spent each year on salts such as sodium chloride for deicing highways. It would thus be advantageous if the salts in waste water could be used for sealing soils to prevent runoff of rain or for sealing the bottom of ponds which collect runoff from various sources.
Finally, it would be desirable if the aforementioned objective could be accomplished while overcoming a problem (expensive to remedy) facing this country and the rest of the world— the disposal of waste waters.